Skin is a very important tissue, which protects a human body by being exposed to external environment and also has biochemical and physical functions. This tissue is composed of three primary layers: epidermis, dermis and hypodermis. The human skin color is determined depending on red blood cells in blood, carotene and melanin in combination, but the skin color differences between races or hyperpigmentation such as chloasma and freckle are mainly caused by melanin. The melanin residing in the epidermis, which is an outer skin layer, is synthesized by a process comprising the following steps: 1) an amino acid, tyrosine is converted into DOPA and then DOPA quinone by an enzyme tyrosinase, and 2) DOPA quinone is subjected to a non-enzymatic oxidation. It has a useful role in blocking ultraviolet light to protect the skin organ below the dermis.
However, the melanin, which is created by means of internal or external stress-based stimulus, is a stable substance which remains until it is discharged to the outside through a skin horning process even when the stress disappears. In addition, the melanin generation may increase through an in vivo polymerization-oxidation process using an enzyme such as tyrosinase as a catalyst when the generation of free radicals increases in skin, inflammatory response occurs, or UV light is applied. In particular, the UV light stimulates the melanin generation, and the partially increased melanin causes chloasma, etc., and undesired problem on skin aesthetically.
For this reason, as an inhibitor of melanin generation, hydroquinone, kojic acid, arbutin, glutathione or vitamin C (ascorbic acid), etc. has been used as a cosmetic ingredient, but theses inhibitors have disadvantages of unsatisfactory whitening effect, instability and severe skin stimulation.